The historical Washington State University Sweet Cherry Breeding Program, led by Dr. Thomas Toyama from 1963 to 1985, developed important and distinct vars and 30 remaining selections contribute significantly to commercial production worldwide and current breeding. However, the origins of this valuable 'Toyama germplasm' are unclear. This study relied on hand-written breeding records of crosses and verified pedigree information to analyze the output of this historical breeding program and characterize the genetic origins of Toyama's germplasm. Dr. Toyama used 103 unique parents from diverse origins to create 241 families, and at least 5,182 germinated seeds formed from at least 88,000 pollinated flowers. Most parents were from North America, especially the most-used 'Stella' that generated half of all germinated seeds. Half of the Toyama germplasm's ancestry was traced to pre-1900 European cultivars, with 'Napoleon' representing 25%-33% of the genetic background. For extant selected germplasm, 'Stella' and two of Toyama's own selections were the most used parents, accounting for 52% of recorded parentages. Similar ancestry contributions for selected and pre-selected germplasm indicate that the diverse germplasm accessed persists in extant breeding parents and commercial cultivars. Exploitation of self-fertility and Toyama's signature complementing of 'Stella' with early-season French cultivars could explain the high success rates of pollinated flowers converted into germinated seeds and eventually into cultivars. DNA-based diagnostics could further reveal the ancestry and valuable alleles of this germplasm to inform future breeding endeavors.

Berry skin color CIE parameters, pH and anthocyanidin profiling of 46 grape accessions were investigated using CIE Lab system, pH measurement and anthocyanidin profiling. CIE parameters separated the samples into three groups: yellowish-green, pinkish-red, and purplish-black, and principal component analysis confirmed clear clustering, with the first two components explaining 99.1% of the variance. After anthocyanidin analysis, cyanidin was detected in all samples, whereas trace-level pelargonidin derivatives were identified by UPLC-MS/MS. Total anthocyanidin content was insufficient to evaluate the quality of berry color, but anthocyanidin composition and relative proportions showed a stronger association with color classification. Yellowish-green berries were enriched in cyanidin, while purplish berries contained more malvidin- and cyanidin. Multivariate analysis identified cyanidin, malvidin, and peonidin derivatives as the main drivers of berry skin color variations. Skin homogenate pH ranged from 3.36 to 4.63 and it was lower in wild grape relatives. Correlation analysis indicated that pH was associated with color parameters. Species-related differences in anthocyanidin glycosylation and acylation were evident, and mono/diglucosides may have potential effects on skin color. Overall, skin color appears to depend on anthocyanidin composition, relative proportions, and pH, offering a chemical basis for grape breeding and fruit quality evaluation.

The rapid development of viticulture in subtropical regions represents a significant achievement in China’s table grape industry over the last two decades. However, insufficient winter chilling in these areas often leads to inadequate dormancy, which compromises nutrient translocation and storage in grapevines. Insufficient chilling accumulation results in asynchronous budbreak and reduced cane quality. In this study, ‘Shine Muscat’ grapevines were used to systematically evaluate how different defoliant agents affect budbreak characteristics from the perspective of nutrient translocation and storage. The results indicated that applications of ethephon or urea alone, as well as their combinations with boric acid, yielded unstable effects, often causing primary bud necrosis, decreased flower formation rates, and phytotoxicity. In contrast, the combination of lime sulfur and boric acid exhibited a remarkable synergistic effect, significantly promoting dry matter and starch accumulation in canes while enhancing the budbreak speed, uniformity, and flower cluster formation rate. Further experiments with varying concentrations of lime sulfur combined with 0.2% boric acid revealed that utilizing 2% lime sulfur in this combination produced the most pronounced effects, achieving the highest dormancy-breaking efficacy under conventional cultivation conditions. This treatment was used for the first time to produce a second crop during off-season cultivation. The dual effects of dormancy release and bud promotion achieved via this approach represent a reliable solution in high-quality and efficient grape production in subtropical regions.

Mature Vitis davidii berries exhibit a unique metabolite profile characterized by exceptionally low malate, relatively lower soluble sugars, and abundant anthocyanin diglucoside accumulation. To elucidate the regulatory basis underlying these distinctive traits, we performed an integrated transcriptomic and metabolomic analysis across 18 developmental stages. This atlas identified veraison as a critical metabolic reprogramming window, marking a significant shift in metabolic flux that is potentially linked to species-specific transcriptional divergences. Using weighted gene coexpression network analysis (WGCNA), we identified candidate hub genes hypothesized to participate in these shifts. Specifically, transient transformation in grapevine callus provided preliminary functional evidence suggesting that the nuclear-localized transcription factor VdNAC17 potentially regulates soluble sugar accumulation, while VdbZIP30 might serve a dual regulatory function coordinating both soluble sugars and anthocyanins. Collectively, this high-resolution multiomics atlas proposes a foundational regulatory framework for V. davidii berry quality and identifies promising genetic targets for targeted grapevine breeding programs.

[Objective]Vitis davidii.is an important wild grape germplasm resource in southern China.The organic acids in its fruits primarily accumulate in the form of tartaric acid,malic acid and citric ac-id in the vacuoles during the early stages of fruit development,a process primarily influenced by alumi-num-activated malate transporter(ALMT9),vacuolar membrane dicarboxylate transporter(tDT),and vacuolar membrane proton pump.This study aimed to investigate the function of the VdWRKY26 gene in the growth and development of Vitis davidii fruits.The coding region(CDS)and promoter sequence of the VdWRKY26 gene were cloned from Xiangci No.1,and its function and promoter activity were further analyzed.[Methods]The Pearson correlation coefficients between VdWRKY26 gene expression data and organic acid content were calculated using the R language packages GGally and ggplot2.Us-ing cDNA from Vitis davidii fruits tissue as a template,primers were designed via the Oligo7 website for PCR amplification.The CDS region of the VdWRKY26 gene was cloned via reverse transcription polymerase chain reaction(RT-PCR).The phylogenetic tree and multiple amino acid sequence align-ments of the VdWRKY26 gene and its homologous were constructed using TBtools,MEGA 12.0,and DNAMAN software.Following the construction of a GFP-VdWRKY26 expression vector,it was trans-formed into tobacco to determine the subcellular localization of VdWRKY26.The expression levels of VdWRKY26 were measured by qPCR in different tissues of V davidii,and the promoter activity of Vd-WRKY26 was determined by GUS staining.Homologous expression in grape 41B suspension cells was used to validate its function.[Results]Pearson correlation analysis between VdWRKY26 gene expres-sion levels and organic acid content revealed that VdWRKY26 exhibited high expression during the ear-ly stages of fruit development and low expression during the later stages,showing a significant positive correlation between VdWRKY26 gene expression levels with organic acid accumulation in V.davidii fruits.Sequence analysis indicated that the coding region of VdWRKY26 gene spans 1434 bp,encoding 477 amino acids.Phylogenetic analysis of VdWRKY26 and its homologous genes showed that Vd-WRKY26 belonged to the same clade as petunia PhPH3,pear PbWRKY26 and apple MdWRKY126.Using DNAMAN software to align the VdWRKY26 protein sequence with its homologous sequences from V.vinifera,apple,pear,tomato,Arabidopsis,Petunia,and Citrus,it was found that this protein contains a WRKY domain encompassing the β2,β3 and β4 regions.Subcellular localization analysis re-vealed that the GFP-VdWRKY26 protein was primarily localized in the nucleus.Subsequently,qPCR was used to detect the expression levels of VdWRKY26 in roots,stems,young leaves,fruits at 13 days after flowering(DAF),fruits at 49 DAF,fruits at 88 DAF,and fruits at 130 DAF.Results revealed that VdWRKY26 exhibited higher expression levels in leaves,fruits at 13 days after flowering(DAF),and fruits at 49 DAF,while showing relatively lower expression in roots and stems.This indicates that the gene may play a key regulatory role during the early stages of leaf and fruit development.Analysis of ciss-acting elements in the VdWRKY26 promoter via the PlantCARE website predicted that this promoter primarily contains the light-responsive element Box4 and participates in drought-induced elements such as MBS.Subsequently,transient transfection was performed in tobacco plants followed by GUS stain-ing analysis.Results showed distinct blue staining in leaves at the transfection site,while no staining was observed in the empty vector control group,confirming the activity of the cloned VdWRKY26 gene promoter.Homologous expression of the VdWRKY26 gene was performed in grape 41B suspension cells,using empty vector-transformed grape 41B cells as controls.The expression levels of the Vd-WRKY26 gene in the control group(EV)and VdWRKY26 transgenic grape 41B cells was detected by qPCR.Results showed that the expression level of VdWRKY26 in the transgenic grape 41B cells was on-ly 32.135％of that in the empty vector transgenic control cells,indicating a co-suppression phenome-non.High-performance liquid chromatography was used to determine the organic acid content in EV and 35S:GFP-VdWRKY26 transgenic grape 41B cells.It was found that the malic acid content in 35S:GFP-VdWRKY26 transgenic grape 41B cells was significantly lower than that in the control group,while the citric acid content showed no significant changes.This confirmed that VdWRKY26 primarily participates in the regulation of malic acid accumulation in grapes.[Conclusion]This study cloned the CDS region and promoter sequence of the VdWRKY26 gene and analyzed its function.VdWRKY26 ex-hibits higher expression levels in leaves and fruits than that in roots and stems,showing high expression levels during the early stages of fruit development.The cloned 2545 bp promoter sequence of the Vd-WRKY26 gene exhibits promoter activity.The VdWRKY26 protein is localized in the cell nucleus and possesses the function of regulating malic acid accumulation in grapes.

Aroma and texture are two key factors determining peach fruit quality. However, the specific gene loci that coordinately regulate both traits simultaneously remain largely unclear. In this study, a multi-omics strategy integrating GC-MS, RNA sequencing (RNA-seq) and genome re-sequencing was used to identify differentially accumulated volatile metabolites and differentially expressed genes (DEGs) between two peach cultivars with contrasting fruit texture at six ripening stages. Allelic variations were further validated in a panel of 54 peach accessions. The objectives were to identify novel genes and their regulatory interactions related to the above traits, and to uncover useful allelic variations or haplotype that can be developed as molecular markers for peach breeding. Phenotypic analysis showed that fruit firmness in the slow-ripening cv. 'SAAS 030 ' significantly decreased during late ripening stages, whereas that in the stony hard cv. 'BRY' remained relatively stable. Targeted metabolomics analysis quantified 39 VOCs and 37 non-VOCs, among which lactone contents were positively correlated with D-galacturonic acid. All six lactones significantly increased during the ripening in 'SAAS 030 ', but showed little change in 'BRY'. Similarly, transcript level of 23 DEGs increased gradually during ripening in 'SAAS 030 ', but remained relatively constant in 'BRY'. Comparative analysis of resequencing data from 54 peach accessions identified five SNP loci (SNP_14092032_A/G, SNP_14092292_T/C, SNP_18844192_G/ T, SNP_18854859_C/T, SNP_18857454_T/C) distributed across two functional genes, PpYUC11 and PpACX2. These SNPs formed into six haplotype patterns that were simultaneously associated with both lactone content and fruit texture. These results provide valuable molecular resources for developing breeding tools to improve the efficiency and precision of peach quality breeding.

Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), severely restricts the sustainable development of the kiwifruit industry. Screening stable resistant germplasm and establishing efficient disease resistance evaluation methods are core prerequisites for breeding resistant cultivars. In this study, 86 Actinidia accessions were systematically assessed for Psa susceptibility over three consecutive years using the reported detached shoot inoculation assay. Seven representative accessions with contrasting resistance phenotypes, namely ‘Cuiyu’, ‘Chuhong’, ‘Jinmei’, ‘Hongyang’, ‘Cuixiang’, ‘Avfs08’, and ‘G3’, were selected to measure the activities of four defense-related enzymes post Psa inoculation to dissect the physiological mechanisms driving divergent Psa resistance in kiwifruit. Lesion lengths across years exhibited a significant positive correlation, demonstrating that this inoculation method delivers repeatable, genetically stable phenotypic data with limited environmental interference. Two accessions belonging to A. valvata and A. eriantha exhibited stable high resistance via synergistic biochemical defenses. By contrast, the widely grown cultivar ‘Hongyang’ was highly susceptible, while moderately resistant materials such as ‘Cuiyu’ and ‘Yannong 3’ were discovered within the inherently susceptible species A. chinensis. Highly resistant accessions rapidly induced coordinated increases in SOD and PAL activity at 24 h post inoculation to maintain ROS homeostasis and lignin biosynthesis, whereas susceptible accessions displayed chaotic, ineffective enzymatic stress responses. Temporal synergy of PAL and POD may act as the key defensive regulatory mode. This study uncovered substantial interspecific variation in Psa resistance across Actinidia germplasm, identified elite donors with stable resistance, and elucidated the physiological mechanisms of kiwifruit resistance to Psa. These findings provided a theoretical foundation and valuable germplasm for subsequent resistance gene mining and disease resistance breeding.

High temperature is one of the major natural problems resulting in delayed growth, development and decreased agricultural productivity. Kiwifruit is highly sensitive to high temperature at its entire development stage. In order to better understand the kiwifruit physiological and molecular mechanism, we conducted out a physiological parameters and transcriptome analysis under high temperature conditions using the leaf tissues of two species viz., thermosensitive Actinidia chinensis cv. Hongyang (Ac) and thermotolerant type Actinidia eriantha cv. Huate (Ae). The leaves from Ae plants were characterized as the underside leaf was covered by long and density intertwining trichome, thicker leaf tissues, low stomatal density when comparing with those from the Ac plants. When exposure to high temperature, the Ae plants maintained stabler photosynthesis and scavenged excess ROS by accumulating lower H2O2 capacity and increasing antioxidant capacity, significantly induced expression of antioxidant-related genes in comparison with the Ac plants. Moreover, global transcriptome profiling demonstrated that induced expression of genes related to endoplasmic reticulum (including heat shock protein), Ca2+ signaling pathway, glutathione metabolism, which might contribute to improved thermotolerance in Ae plants. Above findings suggest that the significantly enhanced thermotolerance of Ae plants might attribute to leaf morphologic variation, stabled photosynthetic and improved antioxidant capacities, significantly induced higher differentially expressed genes (DEGs), such as HSP genes. Taken together, our results provide a dependable and useful information on the heat response in kiwifruit plants.

Somatic embryogenesis is a crucial genetic transformation method in plants. Despite numerous studies being conducted for acquiring embryogenic competence in plant cells, somatic embryo (SE) induction from embryogenic cells (ECs) has attracted relatively limited research attention. In grapes, somatic cell induction is impeded by unidentified inhibitors, which hinders the progression of globular embryo (GE) formation and subsequently embryo development. We found that addition of activated charcoal (AC) to the grape SE induction medium augmented the speed, consistency, and synchronization of embryogenesis. Cell samples cultured in the induction medium with and without AC were thoroughly evaluated through histological anatomy analysis, subcellular structure observation, and comparative transcriptomic analysis. The histological observation revealed the specific timeline of SE formation. An intermediate developmental state, referred to as the globular embryo precursor (PGE), was observed during the induction of GE formation from EC. Members of transcription factor families such as WRKY, MYB, MADS, AP2/ERF, HB-KNOX, HB-HD-ZIP, HB-WOX, NAC, and GRF were identified in the early and middle stages of GE formation. Additionally, we explored the key roles of reactive oxygen species (ROS)-, starch-, cell wall-, and hormone-related genes. The cell wall-related genes were highly enriched in differentially expressed gene sets. Several amyloplasts in EC disappeared, potentially because of hydrolysis, and numerous mitochondria were observed. In AC-added samples, starch was consumed more, and cellulose hydrolysis-related genes were downregulated, whereas cellulose synthesis-related genes had higher expression than AC-free samples. ROS response-related genes were induced when GE induction was initiated. When applied, an optimal concentration of external H2O2 promoted SE initiation in grapes, whereas a high concentration caused delayed GE formation. This study suggests that, by absorbing and releasing substances, the added AC can create a stable buffer environment for cell survival, protect against excessive ROS- or inhibitor-induced cell damage, and support uninterrupted progress of somatic embryogenesis.

南方地区葡萄栽培面积约为266667万m2,其中"阳光玫瑰"葡萄近年发展迅速,已经成为全国的主栽葡萄品种.在湖南地区,通过错季熟期调控技术,对"阳光玫瑰"进行秋延后或二次果栽培,使优良果产值达到1500kg·667m-2以上,可以实现果实在11月—第2年1月错峰上市,减少了7—8月集中上市的销售压力,同时可提高葡萄价格,增加果农收入.本文主要从土壤管理、肥料的施用与水分管理等方面,分述了"阳光玫瑰"的秋延后二次果的技术,以期为广大中部地区、相近南北纬度的国内外葡萄种植户提供技术参考.

Primary bud necrosis of grape buds is a physiological disorder that leads to decreased berry yield and has a catastrophic impact on the double cropping system in sub-tropical areas. The pathogenic mechanisms and potential solutions remain unknown. In this study, the progression and irreversibility patterns of primary bud necrosis in 'Summer Black' were examined via staining and transmission electron microscopy observation. Primary bud necrosis was initiated at 60 days after bud break and was characterized by plasmolysis, mitochondrial swelling, and severe damage to other organelles. To reveal the underlying regulatory networks, winter buds were collected during primary bud necrosis progression for integrated transcriptome and metabolome analysis. The accumulation of reactive oxygen species and subsequent signaling cascades disrupted the regulation systems for cellular protein quality. ROS cascade reactions were related to mitochondrial stress that can lead to mitochondrial dysfunction, lipid peroxidation causing damage to membrane structure, and endoplasmic reticulum stress leading to misfolded protein aggregates. All these factors ultimately resulted in primary bud necrosis. Visible tissue browning was associated with the oxidation and decreased levels of flavonoids during primary bud necrosis, while the products of polyunsaturated fatty acids and stilbenes exhibited an increasing trend, leading to a shift in carbon flow from flavonoids to stilbene. Increased ethylene may be closely related to primary bud necrosis, while auxin accelerated cell growth and alleviated necrosis by co-chaperone VvP23-regulated redistribution of auxin in meristem cells. Altogether, this study provides important clues for further study on primary bud necrosis.

Grapevines possess a hierarchy of buds, and the fruitful winter bud forms the foundation of the two-crop-a-year cultivation system, yielding biannual harvests. Throughout its developmental stages, the winter bud sequentially undergoes paradormancy, endodormancy, and ecodormancy to ensure survival in challenging environmental conditions. Releasing the endodormancy of winter bud results in the first crop yield, while breaking the paradormancy of winter bud allows for the second crop harvest. Hydrogen cyanamide serves as an agent to break endodormancy, which counteracting the inhibitory effects of ABA, while H2O2 and ethylene function as signaling molecules in the process of endodormancy release. In the context of breaking paradormancy, common agronomic practices include short pruning and hydrogen cyanamide treatment. However, the mechanism of hydrogen cyanamide contributes to this process remains unknown. This study confirms that hydrogen cyanamide treatment significantly improved both the speed and uniformity of bud sprouting, while short pruning proved to be an effective method for releasing paradormancy until August. This observation highlights the role of apical dominance as a primary inhibitory factor in suppressing the sprouting of paradormant winter bud. Comparative transcriptome analysis revealed that the sixth node winter bud convert to apical tissue following short pruning and established a polar auxin transport canal through the upregulated expression of VvPIN3 and VvTIR1. Moreover, short pruning induced the generation of reactive oxygen species, and wounding, ethylene, and H2O2 collectively acted as stimulating signals and amplified effects through the MAPK cascade. In contrast, hydrogen cyanamide treatment directly disrupted mitochondrial function, resulting in ROS production and an extended efficacy of the growth hormone signaling pathway induction.

Cytoplasmic calcium (Ca2+) transients and nuclear Ca2+ oscillations act as hubs during root nodulation and arbuscular mycorrhizal symbioses. Plants perceive bacterial Nod factors or fungal signals to induce the Ca2+ oscillation in the nucleus of root hair cells, and subsequently activate calmodulin (CaM) and Ca2+/CaM-dependent protein kinase (CCaMK). Ca2+ and CaM-bound CCaMK phosphorylate transcription factors then initiate down-stream signaling events. In addition, distinct Ca2+ signatures are activated at different symbiotic stages: microbial colonization and infection; nodule formation; and mycorrhizal development. Ca2+ acts as a key signal that regulates a complex interplay of downstream responses in many biological processes. This short review focuses on advances in Ca2+ signaling-regulated symbiotic events. It is meant to be an introduction to readers in and outside the field of bacterial and fungal symbioses. We summarize the molecular mechanisms underlying Ca2+/CaM-mediated signaling in fine-tuning both local and systemic symbiotic events.

Providing hands-on education for the next generation of plant breeders would help maximize effectiveness of future breeding efforts. Such education should include training in introgression of crop wild relative alleles, which can increase genetic diversity while providing cultivar attributes that meet industry and consumer demands in a crop such as cider apple. Incorporation of DNA information in breeding decisions has become more common and is another skill future plant breeders need. The Palouse Wild Cider apple breeding program (PWCabp) was established at Washington State University in early 2014 as a student-run experiential learning opportunity. The objectives of this study were to describe the PWCabp's approaches, outcomes, and student involvement to date that has relied on a systematic operational structure, utilization of wild relatives, and incorporation of DNA information. Students chose the crop (cider apple) and initial target market and stakeholders (backyard growers and hobbyists of the Palouse region). Twelve target attributes were defined including high phenolics and red flesh. Phase one and two field trials were established. Two promising high-bitterness selections were identified and propagated. By running the PWCabp, more than 20 undergraduate and graduate students gained experience in the decisions and operations of a fruit breeding program. PWCabp activities have produced desirable new germplasm via utilization of highly diverse Malus germplasm and trained new plant breeding professionals via experiential learning.

From a tree fruit breeder's perspective, long juvenility represents a significant challenge. Because breeders can only make crosses once trees reach maturity and start to flower, they must often wait through a multi-year juvenile phase before evaluating fruit and making further crosses. Within wild relatives of apple, much useful natural variation exists in length of juvenility. However, the genes and their allelic variation governing the transition from the juvenile to adult phase are not as well elucidated as other valued traits for breeding. Some cross-compatible apple wild relatives transmit short-juvenility alleles to offspring. To identify these genetic factors and their underlying genes, derived families exhibiting variation for length of juvenile phase are needed for QTL analyses. The existing natural genetic variation might then be exploited for apple breeding. Combining genetic factors associated with short juvenility from several distinct sources holds promise for achieving ultra-short juvenility naturally to overcome the problem of long juvenility in apple.

Apple industries suffer from major apple diseases because of widely planted susceptible cultivars. Developed disease-resistant cultivars that often carry only a single source of resistance are not expected to be durable over time. Cultivars with multiple sources of resistance are often commercially unacceptable due to unsatisfactory fruit quality alleles inherited from unimproved and improved parents. To improve fruit quality, approximately five modified backcrossing generations have been used with phenotypic selection for offspring with the least proportion of unimproved genome and elite fruit quality. Modified backcrossing is time-consuming owing to the long juvenility of apple. Unimproved parents are always assumed to carry undesirable alleles in addition to the targeted resistance allele. To efficiently identify favorable offspring each generation, DNA-based markers would be useful. Locus-specific DNA tests are unavailable to detect many sources of resistance alleles. Known numbers of DNA segments from unimproved parents could help subsequent parent selection among offspring because of the direct connection to the probability of eliminating such segments each generation. Accurately estimating the proportion and number of unimproved segments requires precise information on genomic positions of recombinations that can be detected with effective genetic marker sets. High-resolution and genome-wide apple SNP arrays can be used to characterize unimproved DNA segments present in disease-resistant offspring to efficiently achieve durable resistance and elite fruit quality. To hasten apple flowering, a rapid generation cycling approach with transgenic genetic stocks is available. Using these tools is expected to effectively exploit additional unimproved germplasm toward apple genetic improvement.

大树稀植栽培在南方葡萄产区逐渐兴起,为树干输液技术在葡萄精准施肥上的应用提供可能性.采用自流式树干输液技术,以葡萄大树作为试材,采用树干输入1 g/L酸性品红溶液1L,观察品红在叶片、茎干、果实、根系的分布情况;在葡萄果实膨大期树干输入15N标记的硝酸铵溶液,检测输液前和输液后1h、1d、6d、12 d叶片、果实和根系中15N含量.品红试验结果表明:品红在茎干中沿着靠近形成层的木质部进行运输;在叶片中,成龄叶上分布较均匀,幼叶和老叶上呈现不均匀分布;在果实里,膨大期周缘维管束和中央维管束积累较多,转色期和成熟期仅在中央维管束和果刷中积累;根系中主要在木质部积累.”N示踪试验表明:树干输入氮营养液能够在葡萄叶片、果实、根系中进行积累,并且氮在叶片中存在积累和再分配规律,在果实和根系中呈现积累过程.

Apple blue mold causes significant postharvest economic losses worldwide. A blue mold resistance locus, qM-Pe3.1, was previously identified on chromosome 3 of Malus sieversii PI 613981, a wild accession with inferior fruit quality. Introgression of the resistance allele into elite breeding germplasm is difficult and success of introgression and the effect of the PI 613981 genome on fruit quality cannot be phenotypically evaluated until fruiting, which occurs approximately 5 years from seed. In this study, introgression of the qM-Pe3.1 resistance allele was achieved by rapid cycle breeding, utilizing the transgenic line T1190 constitutively expressing the BpMADS4 early-flowering gene. This was supported by DNA-based diagnostic information that enabled marker-assisted selection for blue mold resistance using a locus-specific DNA test developed to detect the qM-Pe3.1 resistance allele in offspring (foreground selection). Of 75 second-generation ([‘Gala’ × PI 613981] × T1190) offspring carrying BpMADS4, 43 also carried the qM-Pe3.1 resistance allele. DNA tests for other trait loci were used to identify other desirable alleles related to fruit quality in progeny and 6874 genome-wide SNP markers (from an apple 20K Illumina® SNP array) were used to identify undesirable genomic segments of PI 613981 (background selection). Three individuals identified with favorable recombination close to qM-Pe3.1 and less than 25% of M. sieversii unimproved genome were selected as best suited for the elimination of unimproved DNA segments in subsequent generations. Our pipeline for introgression of qM-Pe3.1, facilitated by marker-assisted foreground and background selection, successfully advanced this promising germplasm in readiness for the next generation.

Apple trees have a long juvenile period, which makes apple genetic improvement via breeding costly and time-consuming. Transgenic genetic stocks carrying the early-flowering gene BpMADS4 have been used to reduce the juvenility of apple from five or more years to less than 10months. One such genetic stock, T1190, has been used widely in breeding and research. It was reported to be a seedling of Pinova' but the other parent was unknown. Not knowing the alleles that this unknown parent contributed to T1190 brings uncertainties to breeding programs and research studies. In this study, the full pedigree of the genetic stock T1190 was reconstructed using an apple 20K SNP array and a panel of 530 reference cultivars and breeding selections. T1190 was determined to be an offspring of Pinova' and Idared'. The full pedigree of T1190 was used to deduce the mosaic ancestor composition of the transgene-hosting chromosome. Such knowledge is useful to ensure breeding programs and research studies achieve their expected objectives.